1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method therefor, and more particularly, to an image forming apparatus comprising a sample image printing mode for printing plural sample images having different color balances on a piece of printing paper, such as a digital copying machine comprising a mosaic monitor mode, and also an image forming method therefor.
2. Description of the Related Art
A conventional digital color copying machine comprises a reading section for reading an image of a document by using a color image sensor and converting the image of the document into image data for printing, and an electrophotographic printer section for printing an image of the document on a copying paper according to the image data. In the case that plural color images are to be superimposed on a copying paper, the document is read out repeatedly by the reading section, and each color image is printed on the same copying paper by the printer section in the order of respective colors predetermined.
The reading section comprises a masking circuit for generating a color-corrected signal corresponding to printing characteristics of the printer section. Generally speaking, it is difficult for the masking process circuit to minimize the color difference between the real document and the copy thereof with respect to all the colors contained therein. Therefore, in such a case that a copy is further copied as a document, the color tone of the secondary copy may be considerably different from that of the original document. However, in the range of a limited color tone, if a better color balance adjustment is performed, the variation of the color tone can be minimized.
Conventionally, the color balance adjustment is performed by referring to a copy obtained in a certain color balance in a manner of so-called cut and try. In this case, the scanning operation of the document is repeated by a number of times which is a product of a number of times of the color balance operation needed for obtaining a desired color copy and a number of the printing colors, and therefore, the color balance operation is time consuming and laborious.
Generally, in the conventional digital color copying machine, in order to adjust a color balance upon making a color adjustment, for example, there are set respective color adjustment coefficients of cyan color, magenta color and yellow color. Namely, the above color adjustment coefficients are normally set at predetermined standard levels, respectively, and when a color balance of an image to be printed on a copying paper is altered, respective color adjustment coefficients are set at proper levels, respectively.
The inventors of the present invention have proposed a color adjustment selecting method (referred to as a mosaic monitor method hereinafter) for decreasing time and cost required for the color correction in the U.S. patent application Ser. No. 321,405 as filed on Mar. 10, 1989. In this mosaic monitor method, a part of a document (referred to as a specific area hereinafter) including a partial image for example a face of a person, for which the operator makes the color reproduction much particularly, is set by a specific area setting means, and then, image data of the specific area is stored in an image memory means. Next, the color adjustment is made for the image data read out from the image memory means with predetermined various color adjustment coefficients, and then, those image data are printed at different positions of the same copying paper in a mosaic-like pattern. Thereafter, the operator selects an image having a color balance nearest to that of a document or an image having a color balance most desirable for the operator among plural images of the specific area (referred to as mosaic monitor images hereinafter) which have been reproduced with different color balances, respectively. Thereafter, a copy of the whole area of document is produced based on the color adjustment coefficients of the mosaic monitor image selected. Thus, a copy of document having the most desirable color balance can be obtained easily.
In this digital color copying machine using the mosaic monitor method, different plural levels of each of the color adjustment coefficients y.sub.i, m.sub.i and c.sub.i (i=1, 2, 3, . . . ) are set previously, and the color adjustment is made for an image of a partial specific area repeatedly under the condition of plural color balances which have different combinations (y.sub.i, m.sub.j and c.sub.k) of respective set color adjustment coefficients, respectively. Thereafter, the mosaic monitor images comprised of plural test images having different plural color balances is printed on a copying paper, and the operator selects an image having the most desirable color balance among the mosaic monitor images. Thus, it becomes easy for the operator to select an image having the most desirable color balance.
However, for example, if there is no image having a desirable color balance among the mosaic monitor images for the operator, it is necessary for the operator to repeat the above mosaic monitor operation altering the color adjustment coefficients until a mosaic monitor image having a desirable color balance can be obtained. In this case, it is necessary to repeat a scan operation for a specified area of the document image again. Particularly, in the case that the operator wishes to faithfully reproduce an image having a partial image having a skin color such as a portrait, it is often necessary to repeat the color adjustment many times. Therefore, it has been desirable that the color adjustment can be made more efficiently.
Further, in the conventional digital color copying machine, there is often caused a change in the color tone which has been set as the time goes. Therefore, proper color adjustment coefficients may change due to this change. It is desirable that the operator can alter the changed color adjustment coefficients into predetermined proper ones easily.
Furthermore, in the conventional digital color copying machine, the color adjustment coefficients of respective colors can be adjusted, for example, in eleven steps, upon the color adjustment. On the other hand, in the aforementioned mosaic monitor mode, the color adjustment coefficients are relatively roughly changed in several steps in the range of the same color adjustment, for example, in three steps among eleven steps of the same color adjustment, and several mosaic monitor images of a specified area of a document image are printed on a piece of copying paper. Therefore, in the mosaic monitor mode, when the operator selects an image having a desirable color balance among the printed several mosaic monitor images, he can make a more fine color adjustment so as to set a color adjustment coefficient between the adjacent levels thereof which can be set based on the color balance having the selected image among the mosaic monitor images in the mosaic monitor mode, after making the digital color copying machine go back to the next normal mode.
However, in the case of further fine adjusting the color adjustment coefficients which have been selected in the mosaic monitor mode, it is necessary to make the fine color adjustment in a manner of so-called cut and try by more fine adjusting the color adjustment coefficients and performing the copying operation every fine adjustment, after finishing the mosaic monitor mode. Therefore, the above complicated operation is required, and also it takes a long time to more finely adjust the color adjustment coefficients. It is desirable that the color adjustment coefficients can be more finely adjusted in the mosaic monitor mode.
Furthermore, since the operator can not easily grasp a relationship between the color adjustment coefficients and the fine adjustment in the mosaic monitor mode, it is difficult to make the fine color adjustment. If the operator easily grasps this relationship, he can more easily make the fine color adjustment.
Furthermore, in the case of printing the mosaic monitor images in the mosaic monitor mode, a mosaic monitor selection key is pressed, and then, the printing conditions for printing the mosaic monitor images. Thereafter, the printing operation is performed under the printing conditions which have been set by the operator, such as a printing magnification, a size of copying paper, a number of prints. It is to be noted that, since a density different from a predetermined standard value influences the color balance upon printing the mosaic monitor images, the density is reset to the predetermined standard value, and the mosaic monitor images are printed on a piece of copying paper.
However, even though the density is set at the standard value, the operator may set a wrong printing condition upon printing the mosaic monitor image, and also, unsuitable setting values which have been set previously may be used continuously, where that the operator has forgot to set new setting values.
Furthermore, if an all reset key of the digital color copying machine is pressed upon setting the printing conditions, the printing conditions such as a size of copying paper may not always set for suitable printing conditions. In this case, if the set printing magnification is different from the reading magnification for a specified area of a document image, the quality of the printed mosaic monitor images may be different from that of the original image. Further, if the size of the copying paper to be printed is smaller than a size of the printing format of the mosaic monitor images, all the mosaic monitor images may not be printed on the copying paper. Furthermore, if the number of prints which has been set previously is smaller than a number of prints required for printing the mosaic monitor images, all the required copies of mosaic monitor images can not printed on the copying paper. Therefore, if trouble has developed, it is necessary for the operator to select the mosaic monitor mode again, and print the mosaic monitor images on a piece of copying paper. Thus, the operator may waste a time and many pieces of copying papers.